Preparation and characterization of alumina-supported molybdenum carbide Original Research Article

Molybdenum carbide on alumina was studied by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and temperature-programmed surface reaction (TPSR) with hydrogen. The molybdenum carbide was prepared by nitridation of 12.5 wt% MoO3/Al2O3 in a flow of NH3 at 700°C, followed by carburization in a flow of 20% CH4/H2 also at 700°C for 3 h. The sample was compared to an unsupported material prepared from MoO3 in the same manner. The CH4 formation profile during TPSR was deconvoluted into three peaks with maxima at 490°C, 690°C, and 810°C. The peak at 490°C was assigned to reduction of carbidic carbon, and the peaks at 690°C and 810°C were assigned to the removal of pyrolytic and graphitic carbon, respectively, as indicated by XPS and XRD measurements. Overall, the results suggest that molybdenum carbide was formed on the alumina supported by the carburization treatment at 700°C, in the same manner as with an unsupported reference sample. Prenitridation before carburization resulted in the formation of a carbide with a larger surface area and less free carbon, compared to the carbide formed by direct carburization.